In current telecommunications networks, it is possible to automatically forward calls directed to one number to a second number based on certain settings. For example, calls may be forwarded if the number is busy, if the number is not reachable (e.g. a mobile phone with no signal), or if there is no answer within a specified period of time. It is also possible to unconditionally forward all calls directed to a number to a second number. Some network operators may charge the subscriber of the first number for the forwarding service.
The first number may be a virtual number, with no associated destination, which forwards calls to the second number (e.g. a premium rate number which forwards calls to the fixed line telephone number of the business it is registered to).